In the production of a substantially rigid plastic socket for receiving the stump or residual limb of a partial amputee, such as, for example, a prosthetic limb socket as disclosed in U.S. Pat. No. 5,980,803, it is common to extrude a large rectangular flat sheet of thermoplastics material and having a predetermined thickness, such as one-half inch, and then cut the sheet into a plurality of smaller square pieces or sheets, for example, 24 inch square sheets. A peripheral portion of a square sheet is clamped within a square metal clamping frame and the square frame and sheet are placed within an oven having a temperature of about 400xc2x0 F. and until the square plastic sheet softens. The heated square plastic sheet and the attached square frame are then removed from the oven by manually gripping the frame with protective gloves, and the sheet is drawn and stretched downwardly over a hollow positive model of the stump or residual limb.
The positive model is commonly mounted on a vacuum base or pedestal which creates a vacuum within the hollow model and through fine holes or pores within the model while the plastic sheet is stretched over the model to form a socket conforming to the model. The positive model of the patient""s residual limb is commonly produced by forming a plaster cast on the patient""s residual limb, removing the cast after it hardens and filling the cast with a plaster to make a positive model. The cast is then removed or broken away from the positive model with a pneumatic chisel. A positive model may also be made, for example, as disclosed in U.S. Pat. No. 5,901,060, that is, by using a digitized impression of the residual limb to machine the model. After a socket is formed, it usually receives a coupler such as the socket coupler disclosed in U.S. Pat. No. 6,106,559 which issued to the applicant of the present invention.
It has been determined that the above method for making a socket using a square plastic sheet cut from a larger extruded sheet is expensive and results in producing significant scrap from the sheet, primarily due to the square corner portions of the sheet which are scrapped along with the trimmed base portion of the drawn sheet used to form the socket. Also, the clamping frame for the rectangular sheet is relatively expensive, has a limited service life, and requires significant time to be properly attached to the peripheral portion of the square sheet and then removed from the sheet after the heated sheet is stretched over the positive model. The method of making the square sheet, the corner portions of the square sheet and the significant time required for attaching the clamping frame to the square sheet and removing the frame after forming a socket, add significantly to the cost of producing the socket.
The present invention is directed to an improved preform for simplifying the making of a prosthetic limb socket and which significantly reduces the cost as well as the time required for making a prosthetic limb socket in addition to minimizing the equipment required for making a socket. In accordance with a preferred embodiment of the invention, a flat circular disk of thermoplastics material is injection molded in a circular mold cavity having a peripheral portion in which a reinforcing ring is positioned so that the reinforcing ring is embedded within a peripheral portion of the molded disk. The plastic disk with the embedded reinforcing ring forms a preform which is heated within an oven at a temperature of about 400xc2x0 F. and while a peripheral portion of the disk is supported by a flat surface of an aluminum support ring. After the plastics material softens and a center portion of the disk is drooping, the preform is removed from the oven by manually gripping the reinforced peripheral portion of the disk with protective gloves. The preform is then flipped over and moved downwardly over a positive model of a residual limb so that the softened center portion of the disk stretches around the model while a vacuum is applied within the model and through fine or small holes extending through the model to form a plastic socket conforming to the model. After the plastics material cools and becomes rigid, the annular base portion of the disk, including the reinforcing ring, is trimmed from the socket and is discarded.
Other features and advantages of the invention will be apparent from the following description, the accompanying drawing and the appended claims.